chapters/Chapter 4 - Dictionaries.ipynb

{
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Dictionaries\n",
    "\n",
    "<img src=\"./images/dictionary_example.png\" alt=\"dictionary\" style=\"width: 800px;\"/>\n",
    "\n",
    "\n",
    "## How do we (as humans) use a dictionary?\n",
    "\n",
    "We use dictionaries to look up a meaning to a word.\n",
    "Every word that we look up is the **_key_**, and the definition is the **_value_**.\n",
    "\n",
    "You can think of python dictionaries in a similar way. \n",
    "Dictionaries hold content that we need, and we can only access that content through a key."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "\n",
    "## Creating a dictionary\n",
    "\n",
    "You can create dictionaries in a couple of different ways."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### First Way"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'name': 'Kevin', 'breed': 'Bulldog', 'age': 5}\n"
     ]
    }
   ],
   "source": [
    "# Create an empty dictionary\n",
    "animal = dict()\n",
    "\n",
    "# Add key/value pairs\n",
    "animal[\"name\"] = \"Kevin\"\n",
    "animal[\"breed\"] = \"Bulldog\"\n",
    "animal[\"age\"] = 5\n",
    "\n",
    "print(animal)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Second Way"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'name': 'Kevin', 'breed': 'Bulldog', 'age': 5}\n"
     ]
    }
   ],
   "source": [
    "animal = {\n",
    "    \"name\": \"Kevin\",\n",
    "    \"breed\": \"Bulldog\",\n",
    "    \"age\": 5\n",
    "}\n",
    "\n",
    "print(animal)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "\n",
    "## Reviewing Syntax\n",
    "\n",
    "Dictionaries are recognizable by their *__curly braces__*.\n",
    "Lists have *__square brackets__*, dictionaries have *__curly braces__*.\n",
    "\n",
    "Dictionaries look like this:\n",
    "```\n",
    "my_dictionary = { key : value, another_key : another_value }\n",
    "```\n",
    "\n",
    "Both the key and value can be just about anything.. \n",
    "But more often than not, the key will be a string.\n",
    "The key and value are separated by a colon, and the different items in your dictionary are separated by a comma."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "\n",
    "### YOUR TURN\n",
    "\n",
    "Time to create a dictionary!\n",
    "* Create a dictionary where the keys are \"one\" through \"ten\" and the values are 1 through 10, respectively.\n",
    "* Do the inverse!\n",
    "Create a dictionary where the keys are 1 through 10 and the values are \"one\" through \"ten\", respectively."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5, 'six': 6}\n"
     ]
    }
   ],
   "source": [
    "dictionary = {'one' : 1, 'two' : 2, 'three' : 3, 'four':4, 'five':5, 'six':6}\n",
    "print(dictionary)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "\n",
    "## Accessing Values\n",
    "\n",
    "So far, we've created a couple dictionaries. \n",
    "\n",
    "Let's take a look at our animal dictionary again. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'name': 'Kevin', 'breed': 'Bulldog', 'age': 5}\n"
     ]
    }
   ],
   "source": [
    "print(animal)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "A question we may ask is..\n",
    "> **What breed is our animal?**\n",
    "\n",
    "We know that our dictionary has the answer. \n",
    "Just by looking at it, we know it's 'Bulldog'. \n",
    "But, we need to access it programatically. \n",
    "\n",
    "We can access a dictionary's value _by it's key_."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Bulldog\n"
     ]
    }
   ],
   "source": [
    "print(animal['breed'])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**What is the animal's name??**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Kevin\n"
     ]
    }
   ],
   "source": [
    "print(animal['name'])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In our examples, we were able to access our animals different attributes through the key. \n",
    "\n",
    "```python\n",
    "variable[ key ]\n",
    "```\n",
    "\n",
    "Note the square brackets!"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### YOUR TURN\n",
    "\n",
    "* Print out the values for the even numbers of your first number dictionary.\n",
    "* Print out the odd numbers for the other!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one 1\n",
      "two 2\n",
      "three 3\n",
      "four 4\n",
      "five 5\n",
      "six 6\n"
     ]
    }
   ],
   "source": [
    "# Use a for loop\n",
    "dictionary = {'one' : 1, 'two' : 2, 'three' : 3, 'four':4, 'five':5, 'six':6}\n",
    "\n",
    "for key, value in dictionary.items() : \n",
    "    print(key + \" \" + str(value))\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "\n",
    "## Dictionary Methods\n",
    "\n",
    "Just like lists, dictionaries also have _methods_ that we can use.\n",
    "\n",
    "* `clear` - Clears out the keys and values\n",
    "* `get` - A safer way to access a value\n",
    "* `keys` - Returns all the keys in your dictionary\n",
    "* `values` - Returns all the values\n",
    "* `items` - Returns keys and values as pairs!\n",
    "* `update` - Merges two dictionaries together\n",
    "* `pop` - returns a value by key and removes it from the dictionary at the same time\n",
    "\n",
    "Go ahead and run the next cell. \n",
    "See what happens to our dictionary!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Keys --->  dict_keys(['name', 'breed', 'age'])\n",
      "Values ->  dict_values(['Kevin', 'Bulldog', 5])\n",
      "Items -->  dict_items([('name', 'Kevin'), ('breed', 'Bulldog'), ('age', 5)])\n",
      "\n",
      "Name --->  Kevin\n",
      "Dict --->  {'breed': 'Bulldog', 'age': 5}\n",
      "Dict --->  {'breed': 'Bulldog', 'age': 5, 'name': 'Bert', 'owner': 'Ernie'}\n",
      "Animal ->  {}\n"
     ]
    }
   ],
   "source": [
    "print('Keys ---> ', animal.keys())\n",
    "print('Values -> ', animal.values())\n",
    "print('Items --> ', animal.items())\n",
    "\n",
    "name = animal.pop('name')\n",
    "print('\\nName ---> ', name)\n",
    "print('Dict ---> ', animal)\n",
    "\n",
    "animal.update({'name': 'Bert', 'owner': 'Ernie'})\n",
    "print('Dict ---> ', animal)\n",
    "\n",
    "animal.clear()\n",
    "print('Animal -> ', animal)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "\n",
    "### YOUR TURN\n",
    "\n",
    "* Check the keys of your first number dictionary.\n",
    "* Check the values of the same dictionary.\n",
    "* Remove the highest number, and print out the number.\n",
    "Then, print the dictionary to make sure the number is gone.\n",
    "* Merge number dictionary 1 with number dictionary 2 and print it out.\n",
    "* Clear number dictionary 2."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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